The present invention relates to an improved process for preparing vinylpyridine from corresponding picoline. The present invention relates to a process for the preparation of 2-vinylpyridine or 4-vinylpyridine over modified zeolite catalysts. In particular, it relates to method for the synthesis of vinylpyridine from corresponding picoline with formaldehyde in vapour phase in an eco-friendly method with high yield and selectivity.
This invention provides a non-corrosive, eco-friendly process, where the catalyst can be recycled and reused for many times. 2-vinylpyridine and 4-vinylpyridine are useful starting material in polymer industry.
2-vinylpyridine (2-VP) is an important monomer used in synthesizing various polymers. Butadiene and styrene monomers were used with 2-vinylpyridine to form latex terpolymer that bonded fabric cords to the rubber matrix of tires. The addition product of methanol and 2-vinylpyridine, 2-(2-methoxy-ethyl) pyridine is a veterinary anthelmintic. This monomer is prepared commercially by autoclaving acetylene, acrylonitrite using cobaltocene catalyst or oxidative dehydrogenation of 2-ethylpyridine on Crxe2x80x94Nb catalyst (Y. Wakatsuki, synthesis, 1, 26 (1976)). (xe2x80x9cHeterocyclic compounds: Pyridine and Pyridine derivatives part 2, Ed. E. Klingsberg, Chapt. V, p 203). Generally in most of the processes, the synthesis of 2-vinylpyridine is practiced by a two-step procedure, which involves a base catalyzed addition of 2-picoline to formaldehyde to give 2-(2-hydroxy ethyl) pyridine followed by dehydration to 2-vinylpyridine monomer. (S. Yasuda, H. Niwa and O. Tagano, Jpn. Kokai Tokyo, Koho 78, 141281 (1978)). 2-vinylpyridine was prepared with 70.8% selectivity at 35.8% conversion over ZrO2 catalyst (Reddy B. N. and Subrahrnanyam M, Catalysis Present and Future, Eds. Kanta Rao P. and Beniwal R. S. p. 304(1995)). The synthesis of vinylpyridines are also reported by the dehydrogenation of alkyl pyridines over V2O5/MgO and MoO3/MgO catalysts in the presence of O2. The alkylation of pyridine, 2,3, and 4-picolines with methanol as alkylating agent over alkali metal ion exchanged X and Y type zeolites in N2 atmosphere resulted in the formation of side-chain alkylated products like ethylpyridines and vinylpyridines were 22.2, and 5.3% at 82.0% conversion over CsY catalyst from 2-picoline and methanol at 450xc2x0 C. However considerable amounts of ring-alkylated derivatives (lutidines) were formed simultaneously. (Kshiwagi H., Enomoto S., Chem. Pharm. Bull., 30(2), 404(1982)).
The alkylation of picolines with methanol was studied over modified X and Y zeolites in which the major products were ethylpyridine and vinylpyridine (Chem. Pharm. Bull., 30(2), 404, 1982). The yields of ethylpyridine were more when the CsY zeolite was used at 450xc2x0 C. On the other hand the yields of vinylpyridines were more over CsX zeolite at about 425xc2x0 C. The yields of vinylpyridines were  less than 20-25%. The syntheses of vinylpyridines were also reported by the dehydrogenation of alkylpyridines over V2O5/MgO and MoO3/MgO catalysts in the presence of oxygen. However the yields and selectivities of 4-vinylpyridine were lower
The main objective of the present invention is to provide a process for the synthesis of vinylpyridines over modified zeolites in a heterogeneous eco-friendly method.
Another objective of the present invention is to provide a process for the preparation of 2-vinylpyridine in high yield and high selectivity.
Another object of the present invention is to provide a process for the preparation of 4-vinylpyridine in high yield and high selectivity.
Another object of the present invention is to provide a process for the preparation of 2-vinylpyridine from 2-picoline and formaldehyde in the presence of catalyst which comprises ZSM-5 containing one or two element(s) from alkali and/or alkaline earth metal ions, like Na+, K+, Rb+, Cs+, Mg+2, Ca+2, Sr+2, etc., which can be recycled and reused for several times.
Still another object of the present invention is to provide a process for the preparation of 4-vinylpyridine from 4-picoline and formaldehyde in the presence of a catalyst which comprises ZSM-5 containing one or two element(s) from alkali and alkaline earth metal ions, like Na, K, Rb, Cs, Mg, Ca, Sr, Ba etc., which can be recycled and reused for several times.
Accordingly, the present invention provides a process for the preparation of 2-vinylpyridine from 2-picoline and formaldehyde in vapour phase over 2-picoline and formaldehyde in vapour phase over modified zeolite/molecular sieve. The catalyst comprises of particularly ZSM-5 modified with sodium, potassium, rubidium, cesium, magnesium, calcium, and/or barium, etc as cation or species.
The present invention also provides a process for the preparation of 4-vinylpyrdine from 4-picoline and formaldehyde in vapour phase over modified zeolite/molecular sieve. The catalyst comprises of ZSM-5 modified with sodium, potassium, rubidium, cesium, magnesium, calcium or barium.
Accordingly, the present invention provides an improved process for the preparation of vinylpyridine from corresponding picoline over modified zeolite catalyst in vapour phase which comprises reacting picoline with formaldehyde with a molar ratio of formaldehyde to picoline in the range of 1:1 to 4:1, at a temperature ranging between 200xc2x0 C. to 450xc2x0 C., at a weight hourly space velocity in the range of 0.25 hrxe2x88x921-1.00 hrxe2x88x921 over a modified commercial zeolite catalyst to obtain the desired product.
In an embodiment of the present invention provides a process wherein, the vinylpyridine obtained is either 2-vinylpyridine or 4-vinylpyridine.
Still another embodiment, one of the reactant picoline is selected from 2-picoline and 4-picoline.
Still another embodiment, one of the catalyst is prepared by varying alkali and alkaline earth modified with a zeolite catalyst selected from a group consisting of ZSM-5, X, Y, mordenite and MCM-41.
In yet another embodiment, the catalyst used is preferably ZSM-5 pentasil type zeolite.
Yet another embodiment, the modification of the catalyst is carried out by alkali or alkaline earth metal ion selected from the group consisting of Li+, Na+, K+, Rb+, Cs+, Mg+2, Ca+2, Sr+2, Ba+2 or two cation modified ZSM-5 like Csxe2x80x94K-ZSM-5.
Still another embodiment the present invention provides a process, wherein the weight percent of the alkali or alkaline earth metal cation in ZSM-5 is varied from 1 weight percent to 4 weight percent.
Still another embodiment, the precursor to modify ZSM-5 catalyst by potassium ion or other elements is varied like KtOBu, KOH, KF, KNO3, K3PO4 and KOAc to improve the yield and selectivity of vinylpyridine.
Still another embodiment, the calcination temperature of modified zeolite is varied from 400xc2x0 C. to 700xc2x0 C.
Still another embodiment the reaction temperature of the catalytic zone in the process is varied from 200xc2x0 C. to 450xc2x0 C.
Still another embodiment the weight hourly space velocity (WHSV) is in the range of 0.25 to 1.0 hrxe2x88x921.
The following catalysts were used in the present process development HZSM-5 (SiO2/Al2O3=30), NaY (SiO2/Al2O3=5.0), H-Mordenite (SiO2/Al2O3=12), and H-MCM-41 (SiO2/Al2O3=31). Each zeolite was pelleted without binder, crushed and sized 18-30 mesh before the impregnation. The catalysts were modified by using required amount of alkali or alkaline earth cation nitrate by an impregnation method. In the case of potassium, different precursors like KOtBu, KF, KOAc, K3PO4 and KOH were used to modify ZSM-5 (30) catalyst. The required amount of precursor was taken in the form of nitrate or other soluble salts in 30 ml of distilled water. 4.0 g of the meshed catalyst was added to it and kept for soaking for 12 h. Then it was dried at 110xc2x0 C. overnight and calcined at 420xc2x0 C. for 4 h before using for the reaction. In a typical procedure for the synthesis of KOtBu modified ZSM-5 (30) catalyst is as follows, 7 g of HZSM-5 (30) was taken in 250 ml two-necked round bottom flask. Prior to the modification the catalyst was predried in oven at 100xc2x0 C. for 1 h followed by flushing with nitrogen gas to remove the water present in the channels of the catalyst. In another round bottom flask required amount of KOtBu was dissolved in dry DMSO solvent. This solution was added to HZSM-5 (30) catalyst and kept stirring for 24 h in presence of nitrogen atmosphere. After 24 h stirring the resultant mixture was filtered, dried at 120xc2x0 C. overnight and calcined at 400xc2x0 C. for 4 h. The reactions were carried out in a fixed bed, continuous, down-flow pyrex reactor with 20 mm internal diameter at atmospheric pressure. All the catalysts were activated by calcination in a flow of air at 420xc2x0 C. for 4 h and brought to the reaction temperature in situ. The catalyst temperature was measured with a thermocouple placed in the middle of the catalyst bed. A mixture of 2-picoline and formaldehyde were fed from a syringe pump at a rate of 2 ml.hxe2x88x921. The products from the reactor was cooled by circulating ice-cooled water and periodically collected. The quantitative analysis of product was carried out by gas chromatography (G.C.). The samples were analyzed by G.C. (Schimadzu-17A and 14B) fixed with an OV-17 (2 mmxc3x97xe2x85x9xe2x80x3OD) on chromosorb W-HP column and flame ionization detector. The retention times were compared with the authentic compounds. The products were confirmed by mass spectra, GC-mass and NMR techniques. The mass balance was  greater than 90-95%.
The following catalysts were used in the present process development HZSM-5 (SiO2/Al2O3=30), NaY (SiO2/Al2O3=5.0), H-Mordenite (SiO2/Al2O3=12), and H-MCM-41 (SiO2/Al2O3=31). Each zeolite was pelleted without binder, crushed and sized 18-30 mesh before the impregnation. The catalysts were modified by using required amount of alkali or alkaline earth cation nitrate by an impregnation method. In the case of potassium, different precursors like KOtBu, KF, KOAc, K3PO4 and KOH were used to modify ZSM-5 (30) catalyst. The required amount of precursor was taken in the form of nitrate or other soluble salts in 30 ml of distilled water. 4.0 g of the meshed catalyst was added to it and kept for soaking for 12 h. Then it was dried at 110xc2x0 C. overnight and calcined at 420xc2x0 C. for 4 h before using for the reaction. In a typical procedure for the synthesis of KOtBu modified ZSM-5 (30) catalyst is as follows, 7 g of HZSM-5 (30) was taken in 250-ml two-necked round bottom flask. Prior to the modification the catalyst was predried in oven at 100xc2x0 C. for 1 h followed by flushing with nitrogen gas to remove the water present in the channels of the catalyst. In another round bottom flask required amount of KOtBu was dissolved in dry DMSO solvent. This solution was added to HZSM-5 (30) catalyst and kept stirring for 24 h in presence of nitrogen atmosphere. After 24 h stirring the resultant mixture was filtered, dried at 120xc2x0 C. overnight and calcined at 400xc2x0 C. for 4 h. The reactions were carried out in a fixed bed, continuous down-flow pyrex reactor with 20 mm internal diameter at atmospheric pressure. All the catalysts was activated by calcination in a flow of air at 420xc2x0 C. for 4 h and brought to the reaction temperature in situ. The catalyst temperature was measured with a thermocouple placed in the middle of the catalyst bed. A mixture of 4-picoline and formaldehyde were fed from a syringe pump at a rate of 2 ml.hxe2x88x921.
The products from the reactor was cooled by circulating ice-cooled water and periodically collected. The quantitative analysis of product was carried out by gas chromatography (G.C.). The samples were analyzed by G.C. (Schimadzu-17A and 14B) fixed with an OV-17 (2 mmxc3x97xe2x85x9xe2x80x3OD) on chromosorb W-HP column and flame ionization detector. The retention times were compared with the authentic compounds. The products were confirmed by mass spectra, GC-mass and NMR techniques. The mass balance was  greater than 90-95%.